WO2021045051A1

WO2021045051A1 - Tire device

Info

Publication number: WO2021045051A1
Application number: PCT/JP2020/033100
Authority: WO
Inventors: 洋一朗鈴木; 高俊関澤
Original assignee: 株式会社デンソー
Priority date: 2019-09-04
Filing date: 2020-09-01
Publication date: 2021-03-11
Also published as: JP2021037885A; US20220268577A1; JP7367404B2; US11846502B2

Abstract

The present invention has a tire-side device (1) provided on a tire (3) side and a vehicle body-side system (2) provided on a vehicle body side, and discerns a road surface state of a traveling road surface of a vehicle and detects a tire wear state. The tire-side device has: a vibration detection unit (10) that outputs a detection signal according to the magnitude of vibration of the tire; a control unit (11) that has a feature amount extraction unit (11a) for extracting a feature amount for each frequency band from a detection signal obtained during one rotation of the tire; and a first data communication unit (12) that transmits road surface data including the feature amount. The vehicle body-side system has: a second data communication unit (24) that receives the road surface data; a road surface assessment unit (25c) that assesses the road surface state of the traveling road surface on the basis of the road surface data; an integral calculation unit (25d) that uses the feature amount for each frequency band included in the road surface data to calculate an integrated value of the feature amount in a specific frequency band; and a wear determination unit (25e) that detects the tire wear state from the integrated value of the feature amount.

Description

Tire device

Cross-reference to related applications

This application is based on Japanese Patent Application No. 2019-161333 filed on September 4, 2019, the contents of which are incorporated herein by reference.

The present disclosure relates to a tire device having a tire side device and a vehicle body side system and capable of determining a road surface condition and detecting a tire wear condition.

Conventionally, in Patent Document 1, a tire-side device having an acceleration acquisition unit on the back surface of the tire tread is provided, the tire vibration is acquired as acceleration by the acceleration acquisition unit, and the acquisition result is transmitted to the vehicle body-side system to display the road surface condition. A tire device for estimation has been proposed. In this tire device, data on the road surface condition is created based on the vibration waveform of the tire acquired by the acceleration acquisition unit, and the data on each wheel is transmitted to the receiver on the vehicle body side to estimate the road surface condition. There is. Then, in order to realize power saving of the tire side device, the change in the road surface condition is determined, and the acquisition result of the vibration applied to the tire is transmitted from the tire side device to the vehicle body side system at the timing when the road surface condition changes. There is. That is, communication is minimized and power saving is achieved by allowing data transmission to be performed only at the timing when the road surface condition for which the road surface condition is desired to be determined changes.

Japanese Unexamined Patent Publication No. 2018-184101

In recent years, there is a need to detect tire wear conditions as well. Therefore, it is conceivable to detect the tire wear state based on the vibration waveform of the tire acquired by the tire side device. However, in order to implement an algorithm for determining the road surface condition and an algorithm for detecting the tire wear condition in the limited power supply and memory of the tire side device, vibration waveform sampling, storage, and various arithmetic processes are performed. It is necessary to save power and memory by minimizing the number of tires.
An object of the present disclosure is to provide a tire device capable of realizing further power saving and memory saving while enabling detection of a road surface condition and a tire wear condition.

In the tire device according to one aspect of the present disclosure, the tire side device includes a vibration detection unit that outputs a detection signal according to the magnitude of the tire vibration, and a feature amount for each frequency band from the detection signal during one rotation of the tire. It has a control unit having a feature amount extraction unit for extracting tires, and a first data communication unit for transmitting road surface data including the feature amount extracted by the feature amount extraction unit. Further, the vehicle body side system includes a second data communication unit that receives road surface data transmitted from the tire side device, a road surface determination unit that determines the road surface condition of the traveling road surface based on the road surface data, and a frequency included in the road surface data. It has an integration calculation unit that calculates the integrated value of the feature amount in a specific frequency band using the feature amount for each band, and a wear determination unit that detects the tire wear state from the integrated value of the feature amount.

In this way, the road surface condition of the vehicle's running road surface is discriminated and the tire wear condition is detected. Specifically, the road surface data for discriminating the road surface condition is used, and the tire wear state is detected from the integrated value of the feature amount of the specific frequency band in the road surface data. Therefore, it is not necessary to transmit data only for detecting the tire wear state, and it is not necessary to implement an algorithm for detecting the tire wear state on the tire side device, sampling, saving, and various arithmetic processes. It is possible to save power and memory by minimizing the number of tires. Therefore, it is possible to make a tire device that can realize more power saving and memory saving while making it possible to discriminate the road surface condition and detect the tire wear state.

Note that the reference symbols in parentheses attached to each component or the like indicate an example of the correspondence between the component or the like and the specific component or the like described in the embodiment described later.

It is a figure which showed the block composition in the vehicle-mounted state of the tire device which concerns on 1st Embodiment. It is a block diagram which showed the detail of the tire side device and the vehicle body side system. It is sectional drawing of the tire which attached the tire side device. It is the output voltage waveform figure of the acceleration acquisition part at the time of tire rotation. It is a figure which shows the state that the detection signal of the acceleration acquisition part was divided into each time window of a predetermined time width T. The determinants Xi (r) and Xi (r-1) in each section in which the time axis waveform at the time of the current rotation of the tire and the time axis waveform at the time of one rotation before are divided by a time window having a predetermined time width T. It is a figure which showed the relationship between and the distance _Kyz. It is a figure which showed the vibration model of a tire. It is a figure of a general vibration model. It is a figure which shows the result when the frequency characteristic of the vibration level of a tire was investigated for each of a new tire and a worn tire. It is a flowchart of the data transmission process executed by the control part of the tire side device. It is a flowchart of the road surface condition determination and wear detection processing executed by the control part of the vehicle body side system. It is a figure which showed the relationship between the tire groove depth and the integral value of a feature amount. It is a block diagram which showed the detail of the tire side apparatus and the vehicle body side system provided in the tire apparatus of 2nd Embodiment. It is a block diagram which showed the detail of the tire side apparatus and the vehicle body side system provided in the tire apparatus of 3rd Embodiment.

Hereinafter, embodiments of the present disclosure will be described with reference to the figures. In each of the following embodiments, parts that are the same or equal to each other will be described with the same reference numerals.

(First Embodiment)
A tire device having a road surface condition determination function and a tire wear condition detection function according to the present embodiment will be described. The tire device according to the present embodiment determines the road surface condition during traveling based on the vibration applied to the ground contact surface of the tire provided on each wheel of the vehicle, and also notifies the danger of the vehicle and the vehicle movement based on the road surface condition. Control etc. The tire device also detects the tire wear state based on the vibration applied to the ground contact surface of the tire.

As shown in FIGS. 1 and 2, the tire device 100 has a structure including a tire side device 1 provided on the wheel side and a vehicle body side system 2 including various parts provided on the vehicle body side. The vehicle body side system 2 includes a receiver 21, an electronic control device for brake control (hereinafter referred to as a brake ECU) 22, a notification device 23, and the like.

The tire device 100 of the present embodiment transmits data according to the road surface condition while the tire 3 is traveling (hereinafter referred to as road surface data) from the tire side device 1, and receives the road surface data by the receiver 21 to receive the road surface condition. Is determined. Further, since the road surface data includes a component that changes according to the tire wear state, the receiver 21 also detects the tire wear state based on the road surface data. Further, the tire device 100 transmits the determination result of the road surface condition and the detection result of the tire wear state by the receiver 21 to the notification device 23, and the notification device 23 notifies the determination result of the road surface condition and the detection result of the tire wear state. .. This makes it possible to inform the driver of the road surface condition and tire wear condition such as dry road, wet road or icy road, and to the driver when the road surface is slippery or the tire wear is progressing. It is also possible to warn. Further, the tire device 100 transmits the road surface condition to the brake ECU 22 or the like that controls the vehicle motion so that the vehicle motion control for avoiding danger is performed. For example, when freezing, the braking force generated with respect to the amount of braking operation is weakened as compared with the case of a dry road, so that vehicle motion control corresponding to when the road surface μ is low is achieved. .. Specifically, the tire-side device 1 and the receiver 21 are configured as follows.

As shown in FIG. 2, the tire-side device 1 is configured to include an acceleration acquisition unit 10, a control unit 11, and a data communication unit 12, and as shown in FIG. 3, is on the back surface side of the tread 31 of the tire 3. Provided.

The acceleration acquisition unit 10 constitutes a vibration detection unit for detecting the vibration applied to the tire 3. For example, the acceleration acquisition unit 10 is composed of an acceleration sensor. When the acceleration acquisition unit 10 is used as an acceleration sensor, the acceleration acquisition unit 10 is in contact with the circular orbit drawn by the tire side device 1 when the tire 3 rotates, that is, the tire tangent line indicated by the arrow X in FIG. An acceleration detection signal is output as a detection signal corresponding to the vibration in the direction. More specifically, the acceleration acquisition unit 10 generates an output voltage or the like in which one of the two directions indicated by the arrow X is positive and the opposite direction is negative as a detection signal. For example, the acceleration acquisition unit 10 performs acceleration detection every predetermined sampling cycle set to a cycle shorter than one rotation of the tire 3, and outputs it as a detection signal. The detection signal of the acceleration acquisition unit 10 is represented as an output voltage or an output current, but here, a case where it is represented as an output voltage will be given as an example.

The control unit 11 corresponds to the first control unit, is composed of a microcomputer equipped with a CPU, ROM, RAM, I / O, etc., and performs the above processing according to a program stored in the ROM or the like. The control unit 11 is configured to include a feature amount extraction unit 11a, a feature amount storage unit 11b, and a change determination unit 11c as functional units for performing these processes.

The feature amount extraction unit 11a uses the detection signal output by the acceleration acquisition unit 10 as a detection signal representing vibration data in the tire tangential direction, and processes this detection signal to extract the feature amount of the tire vibration. In the case of the present embodiment, the feature amount of the tire G is extracted by signal processing the detection signal of the acceleration of the tire 3 (hereinafter referred to as the tire G). Further, the feature amount extraction unit 11a transmits the data including the extracted feature amount to the data communication unit 12 as road surface data via the change determination unit 11c. The details of the feature amount referred to here will be described later.

The feature amount storage unit 11b stores the feature amount extracted by the feature amount extraction unit 11a one rotation before the tire 3 (hereinafter, referred to as the previous feature amount). Since it can be confirmed by the method described later that the tire 3 has made one rotation, the feature amount for one rotation is stored for each rotation of the tire 3. Regarding the feature amount for one rotation of the tire 3, the data may be updated every time the tire 3 makes one rotation, or the data for a plurality of rotations may be stocked and the most every time the tire 3 makes one rotation. You may want to erase the old data. However, from the viewpoint of saving memory of the control unit 11 in the tire 3, it is preferable to reduce the amount of data to be stocked. Therefore, it is preferable to update the data every time the tire 3 rotates.

The change determination unit 11c is a part that determines whether or not there is a change in the road surface condition and transmits the road surface data to the data communication unit. Regarding the presence or absence of a change in the road surface condition, the change determination unit 11c stores the feature amount extracted by the feature amount extraction unit 11a during the current rotation of the tire 3 (hereinafter referred to as the feature amount) and the feature amount storage unit 11b. The judgment is made based on the previous feature amount of the tire 3. The details of this determination will be described later. Then, when it is determined that the road surface condition has changed, the road surface data is transmitted to the data communication unit 12. Further, if it is determined that the road surface condition has not changed, the road surface data is not transmitted to the data communication unit 12.

The data communication unit 12 is a part constituting the first data communication unit. For example, when the road surface data is transmitted from the change determination unit 11c, the road surface data including the feature amount is transmitted at that timing. That is, the road surface data is transmitted only when the road surface condition changes.

On the other hand, as shown in FIG. 2, the receiver 21 has a configuration including a data communication unit 24 and a control unit 25.

The data communication unit 24 is a part constituting the second data communication unit, and plays a role of receiving the road surface data including the feature amount transmitted this time from the data communication unit 12 of the tire side device 1 and transmitting it to the control unit 25. ..

The control unit 25 corresponds to the second control unit, is composed of a microcomputer equipped with a CPU, ROM, RAM, I / O, etc., and performs various processes according to a program stored in the ROM or the like. The control unit 25 includes a support vector storage unit 25a, a similarity calculation unit 25b, a road surface determination unit 25c, an integration calculation unit 25d, and a wear determination unit 25e as functional units for performing various processes.

The support vector storage unit 25a stores and stores the support vector for each type of road surface. The support vector is a feature quantity that serves as a model, and is obtained by learning using, for example, a support vector machine. A vehicle equipped with the tire-side device 1 is experimentally run according to the type of road surface, and the feature amount extracted by the feature amount extraction unit 11a at that time is learned for a predetermined tire rotation number, and a typical feature amount is learned from the feature amount. Is extracted for a predetermined number of minutes and is used as a support vector. For example, a support vector is obtained by learning a feature amount for 1 million rotations for each type of road surface and extracting a typical feature amount for 100 rotations from the feature amount.

The similarity calculation unit 25b calculates the similarity by comparing the feature amount sent from the tire side device 1 with the support vector for each type of road surface stored in the support vector storage unit 25a. The degree of similarity indicates the degree of similarity with the support vector for each type of road surface, and the higher the degree of similarity, the more similar it is. The details of this similarity will be described later.

The road surface determination unit 25c determines the road surface state using the similarity calculated by the similarity calculation unit 25b. For example, the feature amount is compared with the support vector for each type of road surface this time, and the road surface of the support vector having the highest similarity value is determined as the current traveling road surface.

The integral calculation unit 25d calculates the integral value of the feature amount including the component of the predetermined frequency band from the road surface data. As will be described later, the feature amount included in the road surface data is extracted by dividing the detection signal of the acceleration acquisition unit 10 into sections for each time window having a predetermined time width T and performing frequency analysis in each section. .. Therefore, the feature amount of the component of a predetermined frequency band is included in the extracted feature amount. By extracting the feature amounts of the components of the predetermined frequency band and adding them together, the integrated value of the feature amounts of the predetermined frequency band can be calculated.

The wear determination unit 25e detects the tire wear amount based on the integrated value of the feature amount calculated by the integral calculation unit 25d. The integrated value of the feature amount changes according to the tire wear amount, and has the characteristic that the integrated value becomes smaller as the tire wear amount increases. Therefore, the tire wear amount can be detected based on the integrated value of the feature amount.

Further, when the control unit 25 determines the road surface condition and detects the tire wear amount, the control unit 25 transmits information on the road surface condition and the tire wear amount to the notification device 23, and if necessary, the road surface condition and the tire wear amount are transmitted from the notification device 23. Tell the driver the amount. As a result, the driver will try to drive according to the road surface condition, and if the amount of tire wear is large, the danger of the vehicle can be avoided by replacing the tires. For example, the road surface condition determined through the notification device 23 may always be displayed, or the road surface condition may be determined only when the driving needs to be performed more carefully, such as on a wet road or an icy road. The status may be displayed to warn the driver. Similarly, the tire wear amount may be always displayed through the notification device 23, or the tire wear amount may be displayed only when the tire wear amount is large, or a display prompting tire replacement may be performed. ..

Further, the receiver 21 transmits the road surface condition to the ECU for executing the vehicle motion control such as the brake ECU 22, and the vehicle motion control is executed based on the transmitted road surface condition.

The brake ECU 22 constitutes a braking control device that performs various brake controls. Specifically, the brake ECU 22 controls the braking force by increasing or decreasing the wheel cylinder pressure by driving an actuator for controlling the brake fluid pressure. Further, the brake ECU 22 can independently control the braking force of each wheel. When the road surface condition is transmitted from the receiver 21 by the brake ECU 22, the braking force is controlled as vehicle motion control based on the road surface condition. For example, when the transmitted road surface condition indicates that the road surface condition is a frozen road, the brake ECU 22 weakens the braking force generated with respect to the amount of brake operation by the driver as compared with the dry road surface. As a result, wheel slip can be suppressed and the danger of the vehicle can be avoided.

Further, the notification device 23 is composed of, for example, a meter display or the like, and is used when notifying the driver of the road surface condition or the tire wear condition. When the notification device 23 is composed of a meter display, the driver is placed in a place where the driver can see while driving the vehicle, for example, in the instrument panel of the vehicle. When the receiver 21 notifies the road surface condition and tire wear condition, the meter display displays the road surface condition and tire wear condition in a manner that allows the driver to visually grasp the road surface condition and tire wear condition. The status can be notified.

The notification device 23 can also be configured by a buzzer, a voice guidance device, or the like. In that case, the notification device 23 can aurally notify the driver of the road surface condition and the tire wear condition by a buzzer sound or voice guidance. Further, although the meter display is taken as an example of the notification device 23 that performs visual notification, the notification device 23 may be configured by a display that displays information such as a head-up display.

As described above, the tire device 100 according to the present embodiment is configured. Each part constituting the vehicle body side system 2 is connected through an in-vehicle LAN (abbreviation of Local Area Network) by, for example, CAN (abbreviation of Controller Area Network) communication. Therefore, each part can transmit information to each other through the in-vehicle LAN.

Next, the details of the feature amount extracted by the feature amount extraction unit 11a described above and the determination of the change in the road surface condition by the change determination unit 11c will be described.

First, the feature amount extracted by the feature amount extraction unit 11a will be described. The feature amount referred to here is a quantity indicating the feature of the vibration applied to the tire 3 acquired by the acceleration acquisition unit 10, and is represented as, for example, a feature vector.

The output voltage waveform of the detection signal of the acceleration acquisition unit 10 when the tire is rotating is, for example, the waveform shown in FIG. As shown in this figure, the output voltage of the acceleration acquisition unit 10 reaches a maximum value at the start of ground contact when the portion of the tread 31 corresponding to the arrangement location of the acceleration acquisition unit 10 begins to touch the ground as the tire 3 rotates. Take. Hereinafter, the peak value at the start of grounding at which the output voltage of the acceleration acquisition unit 10 takes a maximum value is referred to as a first peak value. Further, as shown in FIG. 4, when the portion of the tread 31 corresponding to the arrangement portion of the acceleration acquisition unit 10 is not in contact with the ground as the tire 3 is rotated, the acceleration acquisition unit 10 is not in contact with the ground. The output voltage of is the minimum value. Hereinafter, the peak value at the end of grounding where the output voltage of the acceleration acquisition unit 10 takes a minimum value is referred to as a second peak value.

The output voltage of the acceleration acquisition unit 10 takes a peak value at the above timing for the following reasons. That is, when the portion of the tread 31 corresponding to the arrangement portion of the acceleration acquisition portion 10 comes into contact with the rotation of the tire 3, the portion of the tire 3 that has been a substantially cylindrical surface in the vicinity of the acceleration acquisition portion 10 is formed. It is pressed and deforms into a flat shape. By receiving the impact at this time, the output voltage of the acceleration acquisition unit 10 takes the first peak value. Further, when the portion of the tread 31 corresponding to the arrangement portion of the acceleration acquisition portion 10 is separated from the ground contact surface as the tire 3 rotates, the pressure of the tire 3 is released in the vicinity of the acceleration acquisition portion 10 to form a flat surface. Return to a substantially cylindrical shape. The output voltage of the acceleration acquisition unit 10 takes the second peak value by receiving the impact when the shape of the tire 3 returns to its original shape. In this way, the output voltage of the acceleration acquisition unit 10 takes the first and second peak values at the start of touchdown and at the end of touchdown, respectively. Further, since the direction of impact when the tire 3 is pressed and the direction of impact when released from pressing are opposite, the sign of the output voltage is also opposite.

Here, the moment when the portion of the tire tread 31 corresponding to the location where the acceleration acquisition unit 10 is arranged touches the road surface is referred to as the “stepping area”, and the moment when the tire tread 31 is separated from the road surface is referred to as the “kicking area”. The "stepping area" includes the timing of the first peak value, and the "kicking area" includes the timing of the second peak value. Further, the area in front of the stepping area is the "pre-stepping area", and the area from the stepping area to the kicking area, that is, the area of the tire tread 31 where the portion corresponding to the arrangement location of the acceleration acquisition unit 10 is in contact with the ground is "before kicking". The area after the kicking area is referred to as the area after the kicking area. In this way, the period during which the portion of the tire tread 31 corresponding to the arrangement portion of the acceleration acquisition unit 10 touches the ground and the period before and after the contact can be divided into five regions. In FIG. 4, five areas R1 to R5 of the detection signals, "pre-stepping area", "stepping area", "pre-kicking area", "kicking area", and "post-kicking area", are arranged in this order. It is shown as.

Since the vibration generated in the tire 3 fluctuates in each of the partitioned regions and the detection signal of the acceleration acquisition unit 10 changes according to the road surface condition, the detection signal of the acceleration acquisition unit 10 in each region is frequency-analyzed. , Detects the road surface condition on the road surface of the vehicle. For example, in a slippery road surface such as a snow-packed road, the shearing force at the time of kicking decreases, so that the band value selected from the 1 kHz to 4 kHz band becomes small in the kicking region R4 and the kicking region R5. In this way, since each frequency component of the detection signal of the acceleration acquisition unit 10 changes according to the road surface condition, it is possible to determine the road surface condition based on the frequency analysis of the detection signal.

Therefore, the feature amount extraction unit 11a transmits the detection signal of the acceleration acquisition unit 10 for one rotation of the tire 3, which has a continuous time axis waveform, for each time window having a predetermined time width T as shown in FIG. The features are extracted by dividing into a plurality of sections and performing frequency analysis in each section. Specifically, by performing frequency analysis in each section, the power spectrum value in each frequency band, that is, the vibration level in a specific frequency band is obtained, and this power spectrum value is used as a feature quantity.

The number of sections divided by the time window of the time width T is a value that fluctuates according to the vehicle speed, and more specifically, according to the rotation speed of the tire 3. In the following description, the number of compartments for one rotation of the tire is n (where n is a natural number).

For example, the power obtained by passing the detection signal of each section through a plurality of specific frequency band filters, for example, five bandpass filters of 0 to 1 kHz, 1 to 2 kHz, 2 to 3 kHz, 3 to 4 kHz, and 4 to 5 kHz. The spectrum value is used as a feature quantity. This feature amount is called a feature vector, and the feature vector Xi of a certain section i (where i is a natural number of 1 ≦ i ≦ n) is expressed by a _ik indicating the power spectrum value of each specific frequency band. As a matrix whose elements are, it is expressed as follows.

Note that k in the power spectrum value a _ik is the number of specific frequency bands, that is, the number of bandpass filters, and when the band of 0 to 5 kHz is divided into five as described above, k = 1 to 5. Then, the determinant X that collectively shows the feature vectors X1 to Xn of all the sections 1 to n becomes the following equation.

This determinant X is an equation expressing the feature amount for one rotation of the tire. The feature amount extraction unit 11a extracts the feature amount represented by the determinant X by frequency analysis of the detection signal of the acceleration acquisition unit 10.

Next, the determination of the change in the road surface condition by the change determination unit 11c will be described. This determination is made by calculating the degree of similarity using the current feature amount extracted by the feature amount extraction unit 11a and the previous feature amount stored in the feature amount storage unit 11b.

Regarding the determinant X representing the feature amount as described above, the determinant of the feature amount this time is X (r), the determinant of the previous feature amount is X (r-1), and the power that is each element of each matrix expression. the spectral values _{_a ik a} (r) _ik, and expressed by a _{(r-1) ik.} In that case, the determinant X (r) of the feature amount this time and the determinant X (r-1) of the feature amount of the previous time are expressed as follows, respectively.

The degree of similarity indicates the degree of similarity between the features represented by the two determinants, and the higher the degree of similarity, the more similar they are. In the case of the present embodiment, the change determination unit 11c determines the degree of similarity using the kernel method, and determines the change in the road surface condition based on the degree of similarity. Here, the determinant X (r) at the time of this rotation of the tire 3 and the determinant one rotation before are the inner product of X (r-1), in other words, for each time window having a predetermined time width T in the feature space. The distance between the coordinates indicated by the feature vector Xi between the sections divided by is calculated and used as the similarity.

For example, as shown in FIG. 6, regarding the time-axis waveform of the detection signal of the acceleration acquisition unit 10, the time-axis waveform at the time of the current rotation of the tire 3 and the time-axis waveform at the time of one rotation before are each set to a predetermined time width T. Divide into each section by the time window of. In the case of the illustrated example, since each time axis waveform is divided into five sections, n = 5, and i is represented by 1 ≦ i ≦ 5. Here, as shown in the figure, the feature vector Xi of each section at the time of this rotation is Xi (r), and the feature vector of each section at the time of one rotation before is Xi (r-1). _{In that case, regarding the distance Kyz} between the coordinates indicated by the feature vector Xi of each section, the horizontal box including the feature vector Xi (r) of each section at the time of this rotation and the feature of each section at the time of one rotation before. It is shown as a box where a vertical box containing the vector Xi (r-1) intersects. Regarding the distance K _yz , y is a rewrite of i in Xi (r-1), and z is a rewrite of i in Xi (r). In addition, since there is no significant change in vehicle speed between this rotation and one rotation before, the number of compartments at each rotation is basically the same.

In the case of this embodiment, the feature vector is acquired by dividing into five specific frequency bands. Therefore, the feature vector Xi of each section is represented in the 6-dimensional space aligned with the time axis, and the distance between the coordinates indicated by the feature vector Xi between the sections is the distance between the coordinates in the 6-dimensional space. However, the distance between the coordinates indicated by the feature vectors of each section is smaller as the features are similar and larger as they are not similar. Therefore, the smaller the distance, the higher the similarity, and the larger the distance, the more similar. It shows that the degree is low.

For example, when the divisions 1 to n are set by time division, the distance _Kyz between the coordinates indicated by the feature vectors of the divisions 1 is expressed by the following equation.

In this manner, the distance _{K yz} between coordinates indicated by the feature vector of the compartment between time-division determined for all sections, and calculates the distance _{K yz} sum _{K total} of all sections fraction, the sum _{K total} similarity It is used as the corresponding value. Then, the total K _total is compared with a predetermined threshold Th, and if the total K _total is larger than the threshold Th, it is determined that the similarity is low and there is a change in the road surface condition, and the total K _total is smaller than the threshold Th. For example, it is determined that the similarity is high and there is no change in the road surface condition.

Here, the sum K _total _{of the distance Kyz} between the two coordinates indicated by the feature vector of each section is used as the value corresponding to the similarity, but other parameters may be used as the parameter indicating the similarity. .. For example, as a parameter indicating the degree of similarity _{, the average distance Kave} , which is the average value of _{the distance Kyz} _{obtained by dividing the total K total} by the number of sections, can be used. It is also possible to obtain the similarity using various kernel functions, and instead of using all of the feature vectors, the similarity may be calculated by excluding the paths having low similarity from them. ..

Next, the method of calculating the integrated value by the integral calculation unit 25d and the details of the wear determination by the wear determination unit 25e will be described.

As described above, the power spectrum value obtained by passing the detection signal of the acceleration acquisition unit 10 through the filters of a plurality of specific frequency bands is calculated as a feature amount, and is represented by the matrix shown in Equation 1. Become. Therefore, when five bandpass filters of 0 to 1 kHz, 1 to 2 kHz, 2 to 3 kHz, 3 to 4 kHz, and 4 to 5 kHz are used, the first row of the determinant shown in Equation 2 is 0 to 1 kHz. It represents the feature amount of the band, and each line shows the feature amount of each frequency band in order. Further, the first column shows the feature amount in the first time width T of each section divided by a plurality of time widths T, and each column sequentially represents the feature amount in each time width T. Become.

Therefore, the sum of the features of each column in the same row is a value corresponding to the integral value of the features for one rotation of the tire 3 in the frequency band corresponding to that row. The integration calculation unit 25d calculates the sum of the features of each column of the row corresponding to the specific frequency band as the integrated value of the features of the specific frequency band. The specific frequency band referred to here means a high frequency band in which the feature amount changes according to the wear state of the tire 3, and corresponds to, for example, a frequency band of 1 kHz or more. Therefore, the integral calculation unit 25d calculates the integral value of the feature amount in the frequency band of 1 kHz or more. When the bandpass filter of the frequency band described above is used, the integral calculation unit 25d calculates the total value of the sum of the features of each column of the 2nd to 5th rows in the frequency band of 1 kHz to 5 kHz. It is calculated as the integral value of the feature amount of.

Here, the total value of the sum of the features of all frequency bands in the frequency band of 1 kHz or higher is used as the integrated value, but at least the integrated value of a part of the features may be used. That is, it may be the sum of the features of any one frequency band of 1 kHz or higher, or it may be the sum of the features of a plurality of frequency bands.

Here, the reason why the feature amount changes according to the tire wear state and the reason why the change occurs in the high frequency band will be described.

The frequency characteristic of the vibration level in the stepping region and the kicking region of the tire 3 is determined based on the vibration characteristic of the tire 3 including the rubber block, and the vibration level peaks at the natural vibration frequency of the tire 3 including the rubber block. Then, in a frequency band higher than the natural vibration frequency, the vibration level is attenuated due to the vibration isolation effect of the rubber block. The natural vibration frequency of the tire 3 including the rubber block changes according to the wear state of the rubber block, and increases as the wear of the rubber block progresses.

This will be explained with reference to the drawings. FIG. 7 shows a vibration model of the tire 3. The mass of the tread surface 32 of the tire 3 and the rubber block 33 that affects the vibration applied to the tire side device 1 is Mt, the spring constant is Kt, the mass of the rubber block 33 is Mb, the spring constant is Kb, and the damper damping coefficient. Is described as C. In the tire 3, the rubber block 33 serves as a low-pass filter by acting as a vibration-proof material against input vibration from the road surface.

When the tire 3 is new, the groove of the tire tread 31 is deep and the height of the rubber block 33 is high, but as the tire wear progresses, the groove of the tire tread 31 becomes shallow and the height of the rubber block 33 is low. Become. Therefore, as compared with the case where the tire 3 is new, when the tire wear progresses, the mass Mb of the rubber block 33 becomes smaller and the spring constant Kb becomes larger. Then, the function of the rubber block 33 as a low-pass filter is reduced, and the high-frequency component of the tire vibration is increased.

Here, a general vibration model is represented as shown in FIG. 8, and the natural vibration frequency Fn in this vibration model is represented by the following equation. In Equation 1, k is the spring constant of the vibration isolator in the vibration model, and m is the mass of the vibration source.

The spring constant k is calculated by multiplying the Young's modulus determined by the vibration target constituting the vibration model, or the material of the rubber block 33 in the case of the present embodiment, by the area of the vibration target, and the thickness of the vibration target, in other words, the height. Defined as a divided value.

In the vibration model of the tire 3 shown in FIG. 7, the mass Mt is sufficiently larger than the mass Mb, and the spring constant Kt is sufficiently larger than the spring constant Kb. Therefore, it can be regarded as a general vibration model shown in FIG. 8 in consideration of only the mass Mt and the spring constant Kb. That is, the mass m and the spring constant k in Equation 1 can be replaced with the mass Mt and the spring constant Kb in FIG. 7, respectively. When the rubber block 33 is worn and the height is lowered, the mass Mb is reduced and the spring constant Kb is increased accordingly. In this case, the mass Mt does not change so much, and assuming that the spring constant Kb becomes large, the natural vibration frequency Fn shown by the equation 6 increases.

As described above, the frequency characteristic of the vibration level in the stepping region and the kicking region of the tire 3 is determined based on the vibration characteristic of the tire 3 including the rubber block 33, and at the natural vibration frequency Fn of the tire 3 including the rubber block 33. The vibration level peaks. The natural vibration frequency Fn increases as the rubber block 33 wears and the height becomes lower. For example, as shown in FIG. 9, when the tire 3 is new and the groove depth is 8 mm, the natural vibration frequency Fn is 1.0 kHz, and when the tire 3 is worn and the groove depth is 1.6 mm, the natural vibration frequency Fn became 1.5 kHz. The natural vibration frequency Fn has a different value depending on the material of the tire 3 and the like, but regardless of the material of the tire 3, the natural vibration frequency Fn increases as the tire 3 wears.

Therefore, a groove depth that serves as a guideline for replacing the tire 3 is determined, the natural vibration frequency Fn when the groove depth of the tire 3 serves as a guideline for replacement is set as a specific frequency, and a frequency band higher than that is set as a specific frequency band. , The integrated value of the feature amount of the specific frequency band is calculated. For example, if the recommended groove depth for replacement of the tire 3 is 3.0 mm and the depth is used as the groove depth as a guideline for replacement of the tire 3, for example, a feature amount in a high frequency band of 1.0 kHz or higher. It has been confirmed that the differential value of can be calculated.

In this way, since the frequency characteristic of the vibration level of the tire 3 changes according to the tire wear state, the feature amount changes according to the tire wear state. In addition, a change in the feature amount appears particularly in the high frequency band in which the natural vibration frequency of the tire 3 is taken into consideration. Therefore, the integral calculation unit 25d calculates the integral value of the feature amount in the high frequency band.

Subsequently, the operation of the tire device 100 according to the present embodiment will be described with reference to FIG.

In the tire side device 1 of each wheel, the control unit 11 executes the data transmission process shown in FIG. This process is executed at predetermined control cycles.

First, in step S100, the detection signal input process of the acceleration acquisition unit 10 is performed. This process is continued for a period until the tire 3 makes one revolution in the subsequent step S110. Then, when the detection signal of the acceleration acquisition unit 10 is input for one rotation of the tire, the process proceeds to the subsequent step S120, and the feature amount of the time axis waveform of the detection signal of the acceleration acquisition unit 10 for one rotation of the input tire is extracted. The above steps S100 to S120 are performed by the feature amount extraction unit 11a.

It should be noted that the fact that the tire 3 has made one rotation is determined based on the time-axis waveform of the detection signal of the acceleration acquisition unit 10. That is, since the detection signal draws the time axis waveform shown in FIG. 4, one rotation of the tire 3 can be grasped by checking the first peak value and the second peak value of the detection signal.

In addition, the road surface condition appears as a change in the time axis waveform of the detection signal in the period before and after the "stepping area", "pre-kicking area", and "kicking area". Therefore, it is sufficient that the data during this period is input, and it is not always necessary to input all the data of the detection signals of the acceleration acquisition unit 10 during one rotation of the tire. For example, for the "pre-stepping area" and the "post-kicking area", it is sufficient that there is data in the vicinity of the "stepping area" and the vicinity of the "kicking area". Therefore, the region where the vibration level of the detection signal of the acceleration acquisition unit 10 is smaller than the threshold value is detected as a period in the "pre-depression region" and "post-kick region" that is not easily affected by the road surface condition. The signal may not be input.

Further, the feature amount extraction performed in step S120 is performed by the method as described above.

After that, the process proceeds to step S130, and the similarity is obtained by the above-mentioned method based on the current feature amount and the previous feature amount. For example, by comparing the similarity with the threshold value Th, whether or not there is a change in the road surface condition. Is determined. This process is executed by the change determination unit 11c, and is executed based on the current feature amount extracted by the feature amount extraction unit 11a and the previous feature amount stored in the feature amount storage unit 11b in step S150 described later. Will be done.

Then, if an affirmative determination is made in step S130, the change determination unit 11c transmits the road surface data including the feature amount to the data communication unit 12 in order to execute the data transmission in step S140. As a result, the data communication unit 12 transmits the road surface data including the feature amount this time. In this way, the road surface data including the feature amount is transmitted from the data communication unit 12 only when there is a change in the road surface condition, and the data is not transmitted when there is no change in the road surface condition. I have to. Therefore, it is possible to reduce the communication frequency, and it is possible to realize power saving of the control unit 11 in the tire 3.

Finally, the process proceeds to step S150, and the feature amount is stored in the feature amount storage unit 11b as the previous feature amount as the previous feature amount, and the process is completed.

On the other hand, in the receiver 21, the control unit 25 performs the road surface condition discrimination and wear detection processing shown in FIG. This process is executed at predetermined control cycles when a vehicle start switch such as an ignition switch (not shown) is turned on.

First, in step S200, data reception processing is performed. This processing is performed by the control unit 25 taking in the road surface data when the data communication unit 24 receives the road surface data. When the data communication unit 24 is not receiving data, the control unit 25 ends this process without taking in any road surface data.

After that, the process proceeds to step S210, it is determined whether or not the data has been received, and if it has been received, the process proceeds to step S220, and if it has not been received, the processes of steps S200 and S210 are repeated until it is received.

Then, the process proceeds to step S220 to determine the road surface condition. Regarding the determination of the road surface condition, the road surface condition is determined by comparing the feature amount included in the received road surface data with the support vector for each type of road surface stored in the support vector storage unit 25a. For example, this time, the degree of similarity between the feature amount and all the support vectors for each type of road surface is obtained, and the road surface of the support vector having the highest degree of similarity is determined as the current running road surface. Regarding the calculation of the similarity at this time, the same method as the calculation of the similarity between the current feature amount and the previous feature amount may be used in step S130 of FIG.

After that, the process proceeds to step S230, and wear detection is performed. For wear detection, as described above, the integration calculation unit 25d calculates the sum of the features of the specific frequency band shown in Equation 2 as the integration value, and then compares the integration value with the determination threshold value, for example. Will be. For example, since the relationship between the groove depth corresponding to the amount of wear of the tire 3 and the integrated value is shown as shown in FIG. 12, the integrated value at the groove depth as a guideline for replacing the tire 3 is set as the determination threshold value. I will do it. Then, when the integral value calculated by the integral calculation unit 25d becomes equal to or less than the determination threshold value, it is detected that tire wear has occurred.

As described above, the tire device 100 according to the present embodiment determines the road surface condition of the traveling road surface of the vehicle and detects the tire wear condition. Then, the tire wear state is detected by using the road surface data for discriminating the road surface state and using the sum of the feature amounts of the specific frequency band in the road surface data as an integral value. This eliminates the need to transmit data only for detecting the tire wear state. Therefore, it is not necessary to implement an algorithm for detecting the tire wear state on the tire side device 1, and it is possible to save power and memory by minimizing sampling, storage, and various arithmetic processes. Therefore, the tire device 100 can realize further power saving and memory saving while enabling the determination of the road surface condition and the detection of the tire wear state.

Further, when determining the road surface condition, the road surface data including the feature amount this time is transmitted from the tire side device 1 only at the change timing of the road surface condition. Therefore, it is possible to reduce the communication frequency, and further, it is possible to realize power saving of the control unit 11 in the tire 3.

It should be noted that the tire wear state does not have to be detected frequently, and may be detected only once when the vehicle is running, for example, once during the period when the start switch is turned on. Therefore, if the tire wear state is detected using the road surface data for determining the road surface state, there is no problem even if the data is not transmitted only for detecting the tire wear state. Further, as described above, since the road surface data is sent from the tire side device 1 to the vehicle body side system 2 when the road surface condition changes, the tire wear condition is also detected each time, but the tire wear condition is detected. The detection frequency of is may be reduced. Therefore, for example, if the tire wear state has been detected since the start switch was turned on, a flag indicating the tire wear state is set, and if the flag is set, the process of step S230 is performed. It may not be executed.

(Second Embodiment)
The second embodiment will be described. In this embodiment, the tire wear state can be detected in consideration of the vehicle state with respect to the first embodiment, and the other aspects are the same as those in the first embodiment. Only the different parts will be described.

As shown in FIG. 13, the tire device 100 of the present embodiment includes a state acquisition unit 26 in the vehicle body side system 2, so that the vehicle information acquired by the state acquisition unit 26 is transmitted to the control unit 25 via the in-vehicle LAN. I have to. Then, in the control unit 25, vehicle information is added when the road surface determination unit 25c determines the road surface condition or when the wear determination unit 25e detects the tire wear condition.

Vehicle information here means information related to the tire wear state. The information related to the tire wear state is information that affects the detection of the tire wear state, and includes vehicle speed information, acceleration / deceleration information, steering information, road surface information, weather information and position information, temperature information, and the like. .. Vehicle information can be acquired by communicating with various ECUs provided in the vehicle or external devices.

Vehicle speed information is information indicating the vehicle speed of the vehicle. The higher the vehicle speed, the larger the amplitude of the vibration waveform indicated by the detection signal of the acceleration acquisition unit 10. That is, also with respect to the relationship shown in FIG. 12 described above, even if the amount of wear of the tire 3 is the same, the integrated value of the feature amount is high when the vehicle speed is high, and the integrated value of the feature amount is low when the vehicle speed is low. It becomes a value. Therefore, based on the vehicle speed information, the higher the vehicle speed, the larger the integrated value of the feature amount can be calculated. Therefore, the higher the vehicle speed, the higher the judgment threshold value when detecting the tire wear state. On the contrary, the integrated value of the feature amount can be corrected to a small value. Further, if the vehicle speed is equal to or higher than a predetermined speed, it is possible not to detect the tire wear state.

Acceleration / deceleration information is information indicating the acceleration / deceleration of the vehicle. For example, when suddenly accelerating or braking, it may not be possible to accurately detect the tire wear state. Therefore, based on the acceleration / deceleration information, it is possible to detect the tire wear state when the acceleration / deceleration is within the predetermined range and not to detect the tire wear state when the acceleration / deceleration is outside the predetermined range.

Steering information is information on the steering angle of the steering wheel in the vehicle. When the vehicle is turning, it may not be possible to accurately detect the tire wear condition. Therefore, based on the steering information, it is possible to detect the tire wear state when the steering angle is within the predetermined range, and not to detect the tire wear state when the steering angle is outside the predetermined range.

Road surface information is information indicating the state of the road surface on which the vehicle is traveling. For example, it is possible to grasp the road surface condition such as an uneven road such as a gravel road from the road information and the position information obtained from a navigation device or the like. On uneven roads and the like, the effect appears in the detection signal of the acceleration acquisition unit 10, so there is a possibility that the tire wear state cannot be accurately detected. Therefore, based on the road surface information, it is possible to detect the tire wear state on a flat road such as an asphalt road surface, and not to detect the tire wear state on other than the flat road.

Weather information is information that indicates the weather such as fine weather, rainy weather, and snow, and when used together with location information, the weather at the vehicle's driving location can be specified. For example, compared to the case of fine weather, the road surface μ tends to be lower in rainy weather or snow, and the vibration component due to slip may be superimposed on the detection signal of the acceleration acquisition unit 10, and the tire is in a worn state. It may not be possible to detect the detection accurately. Therefore, based on the weather information, it is possible to detect the tire wear state in the case of fine weather, for example, and not to detect the tire wear state in cases other than fine weather such as rainy weather and snow.

Temperature information is information that indicates the outside air temperature. When the outside air temperature is higher or lower than the assumed temperature range, the fluctuation of the spring constant of the tire 3 becomes large and the vibration characteristic of the tire 3 changes, so that it may not be possible to accurately detect the tire wear state. Therefore, based on the temperature information, it is possible to detect the tire wear state when it is within a predetermined temperature range and not to detect the tire wear state when it is outside the temperature range.

In this way, it is possible to detect the tire wear state by adding the vehicle information. This makes it possible to detect the tire wear state more accurately.

Although the case where the vehicle information is used for detecting the tire wear state has been described here, the vehicle information can also be used for determining the road surface condition. In this way, if the vehicle information is used for determining the road surface condition, the road surface condition can be determined more accurately.

(Third Embodiment)
The third embodiment will be described. This embodiment is a modification of the method for detecting a tire wear state with respect to the first and second embodiments, and is the same as the first and second embodiments in other respects. Therefore, the first and second embodiments are the same. Only the part different from the embodiment will be described.

As shown in FIG. 14, in the tire device 100 of the present embodiment, the control unit 25 in the vehicle body side system 2 is provided with an initial value setting unit 25f.

The initial value setting unit 25f stores the first integrated value calculated by the integral calculation unit 25d as the initial value, that is, the integrated value in the state before the tire 3 is worn. For example, the first integrated value detected at the timing of the first running after the vehicle is manufactured is used as the initial value, or it is detected at the timing of the first running when a setting switch (not shown) is pressed when changing tires. The first integrated value obtained can be used as the initial value. The wear determination unit 25e detects the tire wear state from the relative change between the initial value stored in the initial value setting unit 25f and the integrated value of the feature amount calculated by the integration calculation unit 25d. For example, the wear determination unit 25e can determine that the tire wear has progressed when the integral value of the feature amount calculated by the integral calculation unit 25d is reduced by a predetermined ratio with respect to the initial value.

In this way, the initial value setting unit 25f is provided to store the integrated value of the tire 3 before wear as the initial value, and the relative change of the integrated value of the feature amount calculated by the integral calculation unit 25d from this initial value. It is also possible to detect the tire wear state. In this way, the tire wear state can be detected without setting the determination threshold value corresponding to various vehicle types and tire types.

(Other embodiments)
Although the present disclosure has been described in accordance with the above-described embodiment, the present disclosure is not limited to the embodiment, and includes various modifications and modifications within an equal range. In addition, various combinations and forms, as well as other combinations and forms that include only one element, more, or less, are also within the scope of the present disclosure.

For example, in each of the above embodiments, the road surface data is transmitted from the tire side device 1 to the vehicle body side system 2 only when the road surface condition changes. The road surface data may be transmitted at the timing of. For example, the road surface data may be transmitted from the tire-side device 1 to the vehicle body-side system 2 once or a plurality of times each time the tire 3 makes one or a plurality of rotations.

Further, in the above embodiment, the case where the vibration detection unit is configured by the acceleration acquisition unit 10 is illustrated, but the vibration detection unit can also be configured by another element capable of performing vibration detection, such as a piezoelectric element.

Further, in the above embodiment, the control unit 25 of the receiver 21 provided in the vehicle body side system 2 obtains the similarity between the feature amount and the support vector this time, and determines the road surface condition. However, this is also only an example, and the degree of similarity may be obtained or the road surface condition may be determined by the control unit of another ECU, for example, the brake ECU 22.

The controls and methods thereof described in the present disclosure are realized by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. May be done. Alternatively, the controls and methods thereof described in the present disclosure may be implemented by a dedicated computer provided by configuring the processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and method thereof described in the present disclosure may be a combination of a processor and memory programmed to perform one or more functions and a processor composed of one or more hardware logic circuits. It may be realized by one or more dedicated computers configured. Further, the computer program may be stored in a computer-readable non-transitional tangible recording medium as an instruction executed by the computer.

Claims

It is a tire device that determines the road surface condition of the vehicle's running road surface and detects the tire wear condition.
The tire side device (1) provided on the tire (3) side and
It has a vehicle body side system (2) provided on the vehicle body side,
The tire side device is
A vibration detection unit (10) that outputs a detection signal according to the magnitude of the tire vibration, and
A control unit (11) having a feature amount extraction unit (11a) that extracts a feature amount for each frequency band from the detection signal during one rotation of the tire.
It has a first data communication unit (12) that transmits road surface data including the feature amount extracted by the feature amount extraction unit, and has.
The vehicle body side system
A second data communication unit (24) that receives the road surface data transmitted from the tire side device, and
A road surface discriminating unit (25c) that discriminates the road surface condition of the traveling road surface based on the road surface data, and
An integration calculation unit (25d) that calculates the integrated value of the feature amount in a specific frequency band using the feature amount for each frequency band included in the road surface data, and
A tire device including a wear determination unit (25e) that detects a tire wear state from an integrated value of the feature amount.
The vehicle body side system has a state acquisition unit (26) for acquiring vehicle information related to detection of the tire wear state.
The tire device according to claim 1, wherein the wear determination unit detects the tire wear state based on the integrated value of the feature amount and the vehicle information.
The wear determination unit detects the tire wear state based on at least one of vehicle speed information, acceleration / deceleration information, steering information, road surface information, weather information and position information, and temperature information as the vehicle information. 2. The tire device according to 2.
The vehicle body side system has an initial value setting unit (25f) for setting an initial value of an integrated value of the feature amount.
The wear determination unit detects the tire wear state based on the relative change of the integrated value of the feature amount calculated by the integral calculation unit from the initial value, according to any one of claims 1 to 3. The tire device described.
The tire device according to any one of claims 1 to 4, wherein the integral calculation unit calculates an integral value of the feature amount in a frequency band of 1 kHz or more as a predetermined frequency band.
The tire side device is
A feature amount storage unit (11b) that stores the past feature amount extracted by the feature amount extraction unit as a past feature amount, and a feature amount storage unit (11b).
The road surface state is based on the current feature amount and the past feature amount stored in the feature amount storage unit, using the feature amount extracted during the current rotation of the tire by the feature amount extraction unit as the current feature amount. When there is a change in the road surface condition, the change determination unit (11c) causes the tire side device to transmit the road surface data including the feature amount this time.
The tire device according to any one of claims 1 to 5.